Search results for "Fission product"
showing 10 items of 100 documents
Production of neutron-rich isotopes in fission of uranium induced by neutrons of 20 MeV average energy
2000
In the context of a parameter study conducted by several laboratories for future European radioactive beam facilities based on fast-neutron induced fission, in particular for the SPIRAL-II project at GANIL, we have measured the yields of neutron-rich isotopes in the mass range of 88 to 144. These nuclei were obtained as fission products of natural uranium bombarded by neutrons of 20 MeV average energy emitted by a thick carbon target irradiated by 50 MeV deuterons. Yields have been measured using on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections, except for the symmetric region, is similar. Z-distributions of is…
Production of neutron-rich nuclei in fission induced by neutrons generated by the p + 13C reaction at 55 MeV
2003
Cross-sections for the production of neutron-rich nuclei obtained by neutron-induced fission of natural uranium have been measured. The neutrons were generated by bombarding a 13C target with 55 MeV protons. The results, position of the maximum in the (Z, A)-plane, width and magnitude, are very comparable with those where the neutrons are generated by bombardment of natural 12C graphite with 50 MeV deuterons. Depending on the geometry of the converter/target assembly the isotope yields, however, are a factor of 2-3 lower due to less efficient production of neutrons per primary projectile, especially at small forward angles.
Neutron and fragment yields in proton-induced fission of 238U at intermediate energies
2001
The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of 238 U at energies Ep ¼ 20, 35, 50 and 60 MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields ofneutron-rich fission products in the fission of 238 U by 25 MeV protons were measured using an ion guide-based isotope separator technique. The resul…
Level lifetimes in neutron-rich Ru isotopes
1995
The neutron-rich Ru isotopes are situated between the strongly deformed Sr-Zr region with axial deformation of f l _ 0.40 [1] and the spherical Cd-Sn region. Evidence for triaxiality of even-even Ru isotopes has been presented in [2-5], and lifetimes of some of their 2 + states have been measured in fission studies [6-9]. It seems, however, that in these experiments the nearly identical energies of the 2 + ---* 0 + transitions in l~ and 11~ could not be separated. Therefore, high-resolution measurements are required in order to perceive the evolution of deformation with increasing neutron number. So far only few measurements by the delayed-coincidence method [10] have been performed on chem…
New results with stored exotic nuclei at relativistic energies
2004
Recently, much progress has been made with stored exotic nuclei at relativistic velocities ( v c = 0.7 ) . Fragments of 208Pb and 209Bi projectiles and fission products from 238U ions were produced, separated in flight with the fragment separator FRS, and injected into the storage-cooler ring ESR for precision measurements. 114 new masses of neutron-deficient isotopes in the lead region have been measured with time-resolved Schottky Mass Spectrometry (SMS). A new isospin dependence of the pairing energy was observed due to the improved mass accuracy of typically 1.5×10-7 (30 keV). New masses of short-lived neutron-rich fission fragments have been obtained with Isochronous Mass Spectrometry …
Systematics of neutron emission probabilities from delayed neutron precursors
1973
A simple correlation based on the gross theory ofβ-decay is derived between the neutron emission probabilitiesPn of delayed neutron precursors, theirβ-decay energies and the neutron binding energies of the daughter nuclei. The correlation is shown to be valid for delayed neutron precursors among the fission products. ThePn-values of several expected but still unidentified neutron precursors are estimated together with their contributions to the delayed neutron groups in thermal-neutron induced fission of235U. Some aspects of theβ-strength function for transitions into highly excited states are discussed.
Microscopic description of complex nuclear decay: multimodal fission
2009
Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fission for some rutherfordium, seaborgium, and hassium isotopes.
Non-adiabatic treatment of fission mass distribution
1975
The influence of dynamical corrections to fission mass yields has been studied within the frame work of the macroscopic-microscopic approach and solving the time-dependent Schrodinger equation for the asymmetry degree of freedom, treating the fragment separation classically. The results indicate that the actual motion lies in between the adiabatic and sudden approximations. In particular the dynamic effects tend to increase considerably the probability for symmetric fission as compared to the static case.
The ground-state deformation of98Sr
1987
The half-life of the first excited state (21+) of98Sr has been determined through the measurement of delayed γ-γ coincidences at the fission product separator OSTIS to t1/2=2.74(12) ns. This value is smaller than those obtained earlier from β− — conversion electron delayed coincidences and it indicates a stronger collectivity of the 21+→01+ transition in98Sr [B(E2)=98 (3) spu] than in100Sr [B(E2)=79(3) spu] which is normally assumed to be the better rotor.
Odd neutron nuclei near A=100: Rotational bands in103Mo and105Mo populated in the? ? decays of103Nb and105Nb
1984
Theβ − decays of103Nb and105Nb have been studied at the fission product separators JOSEF and LOHENGRIN. Half-lives of (1.5±0.2) s and (2.95±0.06) s, respectively, have been determined for these decays. Fromγ singles andγ-γ coincidence measurements extended level schemes for103Mo and105Mo have been established for the first time. The lowest energy levels of these nuclei are consistent with the interpretation as members of rotational bands built on a 3/2+ [411] Nilsson state. Evidence is presented for the location of the 9/2+ [404] configuration.